Chapter27-Quantitative Genetics.pptx

The location on a chromosome that affects the outcome

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The location on a chromosome that affects the outcome of a quantitative trait is called a quantitative trait locus (QTL) As discussed later, QTLs are chromosomal regions identified by gene mapping A QTL may contain one or more genes Recently, many genetic tools have greatly enhanced our ability to find regions in the genome where QTLs are likely to reside
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The first demonstration that continuous variation is related to polygenic inheritance occurred in 1909 The Swedish geneticist Herman Nilsson-Ehle studied the inheritance of red pigment in the hull of wheat Triticum aestivum P True-breeding red X true-breeding white F 1 Intermediate red F 2 Great variation in redness, plus white
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Scientists later noted that many characters in different species had similar patterns of inheritance
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Geneticists proposed the multiple-gene or multiple-factor hypothesis It implies that many genes or factors contribute to the phenotype in a quantitative way
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The hypothesis embodies the following major points: 1. At least two genes account for the hereditary influence of the phenotype in an additive way 2. Each gene locus may be occupied by either an additive or non-additive allele 3. The effect of additive alleles at each locus is equivalent 4. No allelic pairs exhibit dominance of one allele over another 5. No gene interactions occur among the alleles at different loci in a polygenic series 6. No genetic linkage is exhibited between the genes in a polygenic series
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Example = Hull color in wheat Fig. 27.3 P AABB aabb X F1 AaBb
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